You Should Drain the Battery to Recalibrate It
FALSE: Nickel-cadmium batteries would commonly suffer from an issue known as the memory effect. If you charged and discharged the battery to the same levels consistently, the battery would start to “forget” where the highest and lowest points were. To prevent that from happening, it was recommended to discharge the battery completely, and then charge it completely back to 100% at least once a month. However, we no longer use nickel-cadmium batteries.
Modern batteries are made from lithium-ion. They are more efficient, lighter, last longer and are more powerful even at smaller sizes. The idea of the memory effect is no longer an issue with lithium-ion batteries. You don’t need to drain the battery from empty to full anymore. Charge your iPhone whenever you want.